The computer program listing appendix contained within file xe2x80x9cCodeListing.txtxe2x80x9d on compact disc xe2x80x9c1 of 1xe2x80x9d, which has been filed with the United States Patent and Trademark Office in duplicate, is hereby incorporated herein by reference. This file was created on May 10, 2001, and is 287 kB in size.
This invention relates generally to power controls and more particularly concerns a switched-mode power supply for powering a DC motor.
Most generally available electrical power in the world is delivered as fifty or sixty Hertz (50-60 Hz) alternating current (AC) in the range of one hundred to three hundred volts (100-300V). Such power can be used directly by equipment such as AC motors to cause the motor""s output shaft to rotate. The control of light and relatively inexpensive AC motors is however limited when compared to the possible control of direct current (DC) motors. DC motors exhibit better control at low revolutions-per-minute (rpm), better torque control, and their rotation speeds can more accurately be controlled by regulating the voltage applied to the motor input terminals. The direction of rotation of the DC motor is generally controlled by controlling the polarity of DC voltage applied to the input terminals of the device.
Common DC control arrangements consist of a relay or other switching apparatus to control the applied DC potential, and some form of power regulator to connect portions of the power from a DC supply to the motor. The variable power connection may consist of something as simple as a rheostat or something more complex such as a semiconductor switching arrangement. Although the power couplers may vary in sophistication, the system is basically a source of DC power coupled by a regulator to the motor or other power using device.
DC power is generally used at low voltages and high currents to best perform its allotted tasks. For example, a twenty four Volt (24V) DC motor is easy to control and provides sufficient power for applications such as moving barriers (e.g., garage doors, gates and shutters). Creating such DC voltage from main AC power supplies creates certain difficulties. First, a transformer is needed which is large, heavy and expensive due to its operation at low frequencies. It has been found, however, that large and expensive transformers can be avoided by the use of DC chopper circuits which operate at frequencies above the normal audio frequency range, e.g., forty kilo-Hertz (40 kHz). In such circuits, the AC supplied from main power supplies is first rectified into DC (perhaps with ripple) and then the DC is gated at a high frequency through a relatively small transformer to produce the desired DC power level at the desired voltage range.
Such switched-mode DC power supplies are in use today. They are used, however, in the old manner as a part of the DC supply which is connected to the load (e.g., motor), via a regulating device. The regulation of DC power at the maximum power level creates power and must be done using expensive switching apparatus capable of dissipating considerable power (e.g., switches that are capable of converting excessive power into heat). What is needed in the art, therefore, is a lighter and less expensive method and arrangement for creating DC power and regulating the application of this power to a load.
A method and apparatus for controlling power supplied to a motor is described herein and provides a power controller that is capable of using a smaller, lighter and less expensive transformer and can control motor speed in a more efficient manner by utilizing a minimal amount of components and taking advantage of existing circuit structure. In one form, the apparatus includes a source of electrical power for providing the necessary power to operate the apparatus, a converter for supplying power to a DC motor, an oscillator operating at a relatively higher frequency than the frequency of the electrical power supplied and capable of generating gating signals to the converter, and an inhibitor for inhibiting the generating of gating signals by the oscillator to regulate the power supplied to the motor.
According to a preferred embodiment, an AC input signal is fall wave rectified and supplied to gating circuitry coupled to the converter. The rectified signal is also used to provide power to an oscillator which generates gating signals that drive the gating circuitry coupled to a converter on and off. A switching mechanism is coupled to the oscillator and is utilized to inhibit the oscillator from generating gating signals which in turn prevents the converter from supplying power to a load. In the preferred embodiment, the switching mechanism is a circuit that is capable of inhibiting the oscillator when over current conditions are detected or when a controller detects circuit conditions in which it is desired to regulate the power supplied to the load. Examples of some circuit conditions that may be used to trigger the inhibitor when the load is a DC motor include detected motor speed, movable barrier speed, RPM, movable barrier position, force and limit readings, barrier obstruction readings, and the like.
According to the preferred embodiment the apparatus is setup to keep the oscillator in an OFF state once it has been inhibited, until a desired amplitude of the main AC input signal frequency (or mains frequency) has been reached. Once the desired amplitude has been reached the oscillator is restarted and will remain on until the moveable barrier operator has completed its travel or until another condition for inhibiting the oscillator has been detected. In a particular setting, the oscillator will remain off once inhibited until the input signal""s amplitude reaches zero. Once the amplitude reaches zero, the oscillator is restarted and resumes sending gating signals to the gating circuitry coupled to the converter. This configuration allows for a lighter and less expensive method and arrangement for creating DC power and regulating the application of this power to a load.